The present invention relates to ribbon cartridges which contain a ribbon which is wound on a supply core and which is adapted to be continuously withdrawn from said supply core and from said cartridge case for typing or printing use and to be returned to a take-up core within said cartridge case subsequent to said use.
A wide variety of cartridges of this type are commercially-available for use on a wide variety of typing and printing machines. Reference is made to British Pat. No. 1,559,408 and British Published Application No. 2,003,832A for their disclosure of two of the many types and styles of ribbon cartridges which may be modified to incorporate the novel features of the present invention.
An important problem encountered with ribbon cartridges in which a wound ribbon must be moved from a supply core to a take-up core, passing through a transfer station, is to maintain the ribbon under tension, i.e., prevent it from unwinding from the supply core in the absence of a pulling force of the type exerted by the typing or printing machine. Unless so restrained, the supply core can rotate in increments under the effects of vibration or other forces encountered during handling or shipping of the cartridge and even while the cartridge is mounted on an electric typewriter or printer which vibrates to some extent. Such rotation can cause an excessive slack in the ribbon within or outside the cartridge whereby the ribbon can become tangled or snagged within the cartridge or on the ribbon guides of the typewriter or printer and can break.
Various means are provided in various ribbon cartridges to maintain the ribbon under tension, such as spring arms biased against the ribbon wound on both the supply and take-up spools, a drag means on the ribbon after it leaves the supply spool, a pawl and ratchet on the supply core, etc.
While these devices are effective for their intended purposes, they do present other problems such as multiplicity or complexity of parts, lack of uniformity of tension during use, lack of control of the supply core, and other deficiencies.